1. Field of the Invention
The present invention relates to an amplifier to be mounted in for example, a communications satellite, a radar, or a base station.
2. Background Art
A high-output amplifier with an output of tens of watts or more includes for example, an internally matching type amplifier and a partially matching type amplifier. These amplifiers are not severely demanded to be downsized in comparison to an amplifier for a cell phone. Therefore, in many cases, a distributed constant circuit such as a microstrip line is used for impedance matching, so that power losses are suppressed and the amplifier becomes favorable for wider bandwidth. Unexamined Japanese Patent Application Publication No. H6-318805 discloses an amplifier that transmits a high-frequency signal to a microstrip line.
For example, in a case where the operation frequency is relatively low such as in an L band and an S band, the wavelength of the high-frequency signal is extended. Thus, the line length of the microstrip line required for impedance matching is extended. Therefore, the size of the amplifier is increased.
When the size increase of the amplifier is avoided, patterns for changing the operation frequency cannot be provided and the amplifier cannot correspond to wider bandwidth. In this case, in order to obtain a favorable high-frequency characteristic, a new design of a matching circuit is required for every time the operation frequency is changed by about 100 MHz for example. Thus, there is a problem that the matching circuit is less versatile.